Magnesium oxide and hydromagnesite compounds have many uses and find way into a number of products. Magnesium oxide (MgO) is commonly used in refractory, agricultural, chemical, construction, environmental, and other industrial applications. MgO is used as an insulator in industrial cables, as a basic refractory material for crucibles and as a principal fireproofing ingredient in construction materials. It is used as a reference white color in colorimetry, owing to its good diffusing and reflectivity properties. It is used extensively in heating as a component of tubular construction heating elements. The extensive use is due to its high dielectric strength and average thermal conductivity. MgO doping has been shown to effectively inhibit grain growth in ceramics and improve their fracture toughness by transforming the mechanism of crack growth at nanoscale
In medicine, magnesium oxide is used as an antacid, magnesium supplement, and as a short-term laxative. It is also used to improve symptoms of indigestion. U.S Publication No. 20130059151 discloses use of magnesium oxide for pharmaceutical use wherein magnesium oxide when mixed with a drug that is unstable in acid, demonstrates high stabilizing effects on the drug while also demonstrating superior stability of the magnesium oxide per se.
Hydromagnesite is used in the paper, rubber and plastics industries for various purposes such as coatings, fillers, extenders and pigments for papermaking as well as flame-retardants in electrical wires and cables but also to impart resistance to chemicals in fibers. For example, EP 0 543 262, EP 0 393 813, JP 21 50 436, JP 22 55 843, JP 51 70 984, JP 50 98 085 and KR 2003/0040953 describe flame-retardant compositions comprising hydromagnesite in admixture with other magnesium compounds such as huntite, dolomite and/or magnesium hydroxide.
Hydromagnesite in combination with other magnesium compounds is used in the paper industries in order to impart printability, a high brightness at high opacity, also suitable smoothness and gloss to paper products such as magazines. In this respect, JP 2003/293291 describes coated paper produced by disposing an adhesive and a coating layer consisting mainly of at least one of huntite and hydromagnesite on base paper, wherein the resulting coated paper has high brightness, a high surface-masking effect and excellent printing suitability.
For these compounds, it is important to have a high yield, high purity and superior brightness to enable use in a multitude of industries at a lower cost than existing compounds. In one particular instance, if the quality of the hydromagnesite is high enough, it can be used to replace expensive pigments like titanium oxide.
European application 1984300 discloses a process for preparation of magnesium oxide from the reaction of magnesium salt and alkali/lime. The crude Mg(OH)2 is directly calcined and then treated with water to disintegrate the mass spontaneously to yield a slurry and dissolve away the soluble salts.
U.S. Pat. No. 4,720,375 discloses a process for preparing magnesium oxide by calcining a magnesium ore to obtain magnesium oxide and thereafter leaching at least some of the magnesium oxide with ammonium chloride solution in a recovery stage in order to obtain ammonia and magnesium chloride in solution. Thereafter, the magnesium chloride solution is treated in a precipitation stage in order to precipitate magnesium carbonate trihydrate from the solution while forming ammonium chloride for delivery to the recovery stage and the obtained magnesium carbonate trihydrate is filtered, washed, dried and calcined in order to obtain magnesium oxide of high purity.
Besides the natural hydromagnesite, synthetic hydromagnesite (or precipitated magnesium carbonates) can be prepared. For example, U.S. Pat. Nos. 1,361,324, 935,418, GB 548,197 and GB 544,907 generally describe the formation of aqueous solutions of magnesium bicarbonate (typically described as “Mg(HCO3)2”), which is then transformed by the action of a base, e.g., magnesium hydroxide, to form hydromagnesite.
U.S. Pat. No. 1,163,475 discloses a process for the preparation of basic magnesium carbonate, which comprises treating a magnesium salt solution with ammonium carbonate, while ensuring that in the precipitating medium at least 20% but not more than 85% of ammonia is neutralized by carbonic acid, and that in the reaction mixture there is always an excess of ammonia in comparison to magnesium, and not more than 63 parts by weight of carbonic acid to 24 parts by weight of magnesium. The formed carbonate is extremely voluminous containing more than 50% of water of crystallization, confirming that the formed basic magnesium carbonate is other than hydromagnesite, wherein water is about 15% of the total weight of the compound.
U.S. Pat. No. 5,979,461 discloses a process to prepare compositions containing both, hydromagnesite and magnesium hydroxide, wherein magnesium hydroxide is mixed with water to form a suspension which is further contacted with carbon dioxide and an aqueous basic solution to form the corresponding mixture.
U.S. Pat. No. 8,551,428 discloses a process of preparing hydromagnesite, which comprises a) providing at least one magnesium oxide source, such as magnesium oxide, magnesite, dolomite, huntite, magnesium carbonate, magnesium hydroxide, brucite and mixtures thereof; b) providing gaseous CO2 and/or carbonate-comprising anions; c) slaking of said magnesium oxide source of step a) to convert the magnesium oxide at least partially into magnesium hydroxide; d) contacting the obtained magnesium hydroxide of step c) with said gaseous CO2 and/or carbonate-comprising anions of step b) to convert the magnesium hydroxide at least partially into precipitated nesquehonite; and e) treating the obtained precipitated nesquehonite of step d) in a heat-ageing step.
There is still a need in the art for providing alternative processes for preparing high quality hydromagnesite and magnesium oxide with high levels of purity and brightness. The greater the purity of the magnesium products, the higher the value and suitability for various industries which require very high purity chemicals, such as pharmaceutical industry.